An organic light-emitting display (OLED) device, which is also referred to as an organic electroluminesence display device, is characterized by self-luminous feature. The organic light-emitting display device employs a glass substrate, and a very thin organic material layer which is luminous when an electric current passes through it. The organic light-emitting display device has a wide viewing angle and can significantly save energy, and thereby the organic light-emitting display device has an unparalleled advantage over a conventional display device such as a liquid crystal display device.
In FIG. 1, a schematic diagram of an equivalent circuit of a pixel cell in the organic light-emitting display panel is shown. In FIG. 2, a schematic diagram of a conventional organic light-emitting display panel is shown.
As shown in FIG. 1, in the pixel cell, turning-on and turning-off of a thin film transistor M1 are controlled by a scanning signal scan. When M1 is turned on, a data signal data is transmitted to the gate of a thin film transistor M2 to control a current passing through M2. A power signal PVDD is transmitted through the thin film transistor M2 to a low potential end PVEE to control the luminescence of an organic light-emitting diode oled. The organic light-emitting diode oled is a current-driven device, where a current flowing through the organic light-emitting diode oled may be calculated by the following equation:=½×μ×Cox×W/L×(PVDD−)2,
where μ is the mobility of an active layer; Cox is the capacitance of a capacitor formed by the gate electrode and the active layer; W is the channel width of the organic light-emitting diode; L is the channel length of the organic light-emitting diode; Vdata is the voltage value of the data signal; Vth is the threshold voltage value of the organic light-emitting diode; and PVDD is the voltage of the power signal.
The values for μ, Cox, W, L, and Vth are determined after the size of the organic light-emitting diode oled is determined. As can be seen from the above current equation, in a given oled device, a current flowing through the organic light-emitting diode oled is determined by the power signal PVDD and the data signal Vdata.
Next, referring to FIG. 2, in the organic light-emitting display panel, multiple pixel cells arranged in a matrix are provided in a display region AA. A driving chip Driver IC and power driving chip Power IC are provided on a side of the organic light-emitting display panel. The Driver IC is configured for providing a scanning signal and the data signal to the multiple pixel cells. Generally, only one Power IC is provided in a small-sized organic light-emitting display panel. The Driver IC is provided on the organic light-emitting display panel. The Power IC is provided on a flexible circuit board or a printed circuit board.
The input voltage PVDD is provided by the Power IC to the multiple pixel cells through an input path P for driving the organic light-emitting diode oled for luminescence thereof. Power inputs for supplying voltage PVDD to the multiple pixel cells are connected together throughout the whole display region AA. The voltage may be reduced from a point AA1 which is closest to the Power IC to a point AA2 which is farthest from the Power IC, i.e., the voltage at the point AA1 is higher than the voltage at the point AA2 due to the fact that the organic light-emitting display panel is a current drive device and each pixel cell has resistance, which results in a voltage drop generated when the pixel cells are driven by the current.
The current flowing through the pixel cells decreases gradually with the gradually decreasing voltage from the closest point AA1 to the farthest point AA2, which results in a gradual decrease in the luminance of the organic light-emitting diode oled. In addition, different organic light-emitting diodes oleds have different resistances, and the same organic light-emitting diodes oled may exhibit different resistances when supplied with different driving currents. Therefore, when different organic light-emitting diodes oleds are connected to a power line, the power line varies in the reduction of the voltage, which leads to a difference in the reduction of the luminance of the organic light-emitting diode oled connected to the power line.